xref: /linux/include/linux/pid.h (revision 1e525507)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_PID_H
3 #define _LINUX_PID_H
4 
5 #include <linux/pid_types.h>
6 #include <linux/rculist.h>
7 #include <linux/rcupdate.h>
8 #include <linux/refcount.h>
9 #include <linux/sched.h>
10 #include <linux/wait.h>
11 
12 /*
13  * What is struct pid?
14  *
15  * A struct pid is the kernel's internal notion of a process identifier.
16  * It refers to individual tasks, process groups, and sessions.  While
17  * there are processes attached to it the struct pid lives in a hash
18  * table, so it and then the processes that it refers to can be found
19  * quickly from the numeric pid value.  The attached processes may be
20  * quickly accessed by following pointers from struct pid.
21  *
22  * Storing pid_t values in the kernel and referring to them later has a
23  * problem.  The process originally with that pid may have exited and the
24  * pid allocator wrapped, and another process could have come along
25  * and been assigned that pid.
26  *
27  * Referring to user space processes by holding a reference to struct
28  * task_struct has a problem.  When the user space process exits
29  * the now useless task_struct is still kept.  A task_struct plus a
30  * stack consumes around 10K of low kernel memory.  More precisely
31  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
32  * a struct pid is about 64 bytes.
33  *
34  * Holding a reference to struct pid solves both of these problems.
35  * It is small so holding a reference does not consume a lot of
36  * resources, and since a new struct pid is allocated when the numeric pid
37  * value is reused (when pids wrap around) we don't mistakenly refer to new
38  * processes.
39  */
40 
41 
42 /*
43  * struct upid is used to get the id of the struct pid, as it is
44  * seen in particular namespace. Later the struct pid is found with
45  * find_pid_ns() using the int nr and struct pid_namespace *ns.
46  */
47 
48 #define RESERVED_PIDS 300
49 
50 struct upid {
51 	int nr;
52 	struct pid_namespace *ns;
53 };
54 
55 struct pid
56 {
57 	refcount_t count;
58 	unsigned int level;
59 	spinlock_t lock;
60 	struct dentry *stashed;
61 	u64 ino;
62 	/* lists of tasks that use this pid */
63 	struct hlist_head tasks[PIDTYPE_MAX];
64 	struct hlist_head inodes;
65 	/* wait queue for pidfd notifications */
66 	wait_queue_head_t wait_pidfd;
67 	struct rcu_head rcu;
68 	struct upid numbers[];
69 };
70 
71 extern struct pid init_struct_pid;
72 
73 struct file;
74 
75 struct pid *pidfd_pid(const struct file *file);
76 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
77 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
78 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
79 void do_notify_pidfd(struct task_struct *task);
80 
81 static inline struct pid *get_pid(struct pid *pid)
82 {
83 	if (pid)
84 		refcount_inc(&pid->count);
85 	return pid;
86 }
87 
88 extern void put_pid(struct pid *pid);
89 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
90 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
91 {
92 	return !hlist_empty(&pid->tasks[type]);
93 }
94 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
95 
96 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
97 
98 /*
99  * these helpers must be called with the tasklist_lock write-held.
100  */
101 extern void attach_pid(struct task_struct *task, enum pid_type);
102 extern void detach_pid(struct task_struct *task, enum pid_type);
103 extern void change_pid(struct task_struct *task, enum pid_type,
104 			struct pid *pid);
105 extern void exchange_tids(struct task_struct *task, struct task_struct *old);
106 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
107 			 enum pid_type);
108 
109 extern int pid_max;
110 extern int pid_max_min, pid_max_max;
111 
112 /*
113  * look up a PID in the hash table. Must be called with the tasklist_lock
114  * or rcu_read_lock() held.
115  *
116  * find_pid_ns() finds the pid in the namespace specified
117  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
118  *
119  * see also find_task_by_vpid() set in include/linux/sched.h
120  */
121 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
122 extern struct pid *find_vpid(int nr);
123 
124 /*
125  * Lookup a PID in the hash table, and return with it's count elevated.
126  */
127 extern struct pid *find_get_pid(int nr);
128 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
129 
130 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
131 			     size_t set_tid_size);
132 extern void free_pid(struct pid *pid);
133 extern void disable_pid_allocation(struct pid_namespace *ns);
134 
135 /*
136  * ns_of_pid() returns the pid namespace in which the specified pid was
137  * allocated.
138  *
139  * NOTE:
140  * 	ns_of_pid() is expected to be called for a process (task) that has
141  * 	an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
142  * 	is expected to be non-NULL. If @pid is NULL, caller should handle
143  * 	the resulting NULL pid-ns.
144  */
145 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
146 {
147 	struct pid_namespace *ns = NULL;
148 	if (pid)
149 		ns = pid->numbers[pid->level].ns;
150 	return ns;
151 }
152 
153 /*
154  * is_child_reaper returns true if the pid is the init process
155  * of the current namespace. As this one could be checked before
156  * pid_ns->child_reaper is assigned in copy_process, we check
157  * with the pid number.
158  */
159 static inline bool is_child_reaper(struct pid *pid)
160 {
161 	return pid->numbers[pid->level].nr == 1;
162 }
163 
164 /*
165  * the helpers to get the pid's id seen from different namespaces
166  *
167  * pid_nr()    : global id, i.e. the id seen from the init namespace;
168  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
169  *               current.
170  * pid_nr_ns() : id seen from the ns specified.
171  *
172  * see also task_xid_nr() etc in include/linux/sched.h
173  */
174 
175 static inline pid_t pid_nr(struct pid *pid)
176 {
177 	pid_t nr = 0;
178 	if (pid)
179 		nr = pid->numbers[0].nr;
180 	return nr;
181 }
182 
183 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
184 pid_t pid_vnr(struct pid *pid);
185 
186 #define do_each_pid_task(pid, type, task)				\
187 	do {								\
188 		if ((pid) != NULL)					\
189 			hlist_for_each_entry_rcu((task),		\
190 				&(pid)->tasks[type], pid_links[type]) {
191 
192 			/*
193 			 * Both old and new leaders may be attached to
194 			 * the same pid in the middle of de_thread().
195 			 */
196 #define while_each_pid_task(pid, type, task)				\
197 				if (type == PIDTYPE_PID)		\
198 					break;				\
199 			}						\
200 	} while (0)
201 
202 #define do_each_pid_thread(pid, type, task)				\
203 	do_each_pid_task(pid, type, task) {				\
204 		struct task_struct *tg___ = task;			\
205 		for_each_thread(tg___, task) {
206 
207 #define while_each_pid_thread(pid, type, task)				\
208 		}							\
209 		task = tg___;						\
210 	} while_each_pid_task(pid, type, task)
211 
212 static inline struct pid *task_pid(struct task_struct *task)
213 {
214 	return task->thread_pid;
215 }
216 
217 /*
218  * the helpers to get the task's different pids as they are seen
219  * from various namespaces
220  *
221  * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
222  * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
223  *                     current.
224  * task_xid_nr_ns()  : id seen from the ns specified;
225  *
226  * see also pid_nr() etc in include/linux/pid.h
227  */
228 pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns);
229 
230 static inline pid_t task_pid_nr(struct task_struct *tsk)
231 {
232 	return tsk->pid;
233 }
234 
235 static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
236 {
237 	return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
238 }
239 
240 static inline pid_t task_pid_vnr(struct task_struct *tsk)
241 {
242 	return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
243 }
244 
245 
246 static inline pid_t task_tgid_nr(struct task_struct *tsk)
247 {
248 	return tsk->tgid;
249 }
250 
251 /**
252  * pid_alive - check that a task structure is not stale
253  * @p: Task structure to be checked.
254  *
255  * Test if a process is not yet dead (at most zombie state)
256  * If pid_alive fails, then pointers within the task structure
257  * can be stale and must not be dereferenced.
258  *
259  * Return: 1 if the process is alive. 0 otherwise.
260  */
261 static inline int pid_alive(const struct task_struct *p)
262 {
263 	return p->thread_pid != NULL;
264 }
265 
266 static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
267 {
268 	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
269 }
270 
271 static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
272 {
273 	return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
274 }
275 
276 
277 static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
278 {
279 	return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
280 }
281 
282 static inline pid_t task_session_vnr(struct task_struct *tsk)
283 {
284 	return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
285 }
286 
287 static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
288 {
289 	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
290 }
291 
292 static inline pid_t task_tgid_vnr(struct task_struct *tsk)
293 {
294 	return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
295 }
296 
297 static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
298 {
299 	pid_t pid = 0;
300 
301 	rcu_read_lock();
302 	if (pid_alive(tsk))
303 		pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
304 	rcu_read_unlock();
305 
306 	return pid;
307 }
308 
309 static inline pid_t task_ppid_nr(const struct task_struct *tsk)
310 {
311 	return task_ppid_nr_ns(tsk, &init_pid_ns);
312 }
313 
314 /* Obsolete, do not use: */
315 static inline pid_t task_pgrp_nr(struct task_struct *tsk)
316 {
317 	return task_pgrp_nr_ns(tsk, &init_pid_ns);
318 }
319 
320 /**
321  * is_global_init - check if a task structure is init. Since init
322  * is free to have sub-threads we need to check tgid.
323  * @tsk: Task structure to be checked.
324  *
325  * Check if a task structure is the first user space task the kernel created.
326  *
327  * Return: 1 if the task structure is init. 0 otherwise.
328  */
329 static inline int is_global_init(struct task_struct *tsk)
330 {
331 	return task_tgid_nr(tsk) == 1;
332 }
333 
334 #endif /* _LINUX_PID_H */
335